Chapter 9 Cellular Respiration: Harvesting Chemical Energy

Chapter 9

Cellular Respiration: Harvesting Chemical Energy

Energy flows into an ecosystem as sunlight and leaves as heat

Photosynthesis generates O2 and organic molecules, which are used in cellular respiration

Cellular respiration: Cells use chemical energy stored in organic molecules to regenerate ATP, which powers work

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 9-2

Lightenergy

ECOSYSTEM

Photosynthesis in chloroplasts

CO2 + H2O

Cellular respirationin mitochondria

Organicmolecules+ O2

ATP powers most cellular work

Heatenergy

ATP

Catabolic Pathways and Production of ATP

Fermentation is a partial degradation of sugars that occurs without O2 (no oxygen)

Aerobic respiration consumes organic molecules and O2 and yields ATP (requires O2)

Anaerobic respiration is similar to aerobic respiration but consumes compounds other than O2 (does not require oxygen)


Cellular respiration includes both aerobic and anaerobic respiration but is often used to refer to aerobic respiration

C6H12O6 + 6 O2 6 CO2 + 6 H2O + Energy (ATP + heat)


Redox Reactions: Oxidation and Reduction

The transfer of electrons during chemical reactions releases energy stored in organic molecules

This released energy is ultimately used to synthesize ATP


The Principle of Redox

In oxidation, a substance loses electrons, or is oxidized- The electron donor is called the reducing agent

In reduction, a substance gains electrons, or is reduced - The electron receptor is called the oxidizing agent


becomes oxidized(loses electron)

becomes reduced(gains electron)

becomes oxidized

becomes reduced

The Stages of Cellular Respiration: A Preview

Cellular respiration has three stages: Glycolysis (breaks down glucose into two

molecules of pyruvate) The citric acid cycle (completes the breakdown of

glucose) Oxidative phosphorylation (accounts for most of

the ATP synthesis)


Fig. 9-6-3

Mitochondrion

Substrate-levelphosphorylation

ATP

Cytosol

Glucose Pyruvate

Glycolysis

Electronscarried

via NADH

Substrate-levelphosphorylation

ATP

Electrons carriedvia NADH and

FADH2

Oxidativephosphorylation

ATP

Citricacidcycle

Oxidativephosphorylation:electron transport

andchemiosmosis

The process that generates most of the ATP is called oxidative phosphorylation because it is powered by redox reactions

Oxidative phosphorylation accounts for almost 90% of the ATP generated by cellular respiration


Glycolysis

Glycolysis (“splitting of sugar”) breaks down glucose into two molecules of pyruvate

Glycolysis occurs in the cytoplasm and has two major phases: Energy investment phase (input 2 ATP) Energy payoff phase (produces 4 ATP)


Fig. 9-8

Energy investment phase

Glucose

2 ADP + 2 P 2 ATP used

formed4 ATP

Energy payoff phase

4 ADP + 4 P

2 NAD+ + 4 e– + 4 H+ 2 NADH + 2 H+

2 Pyruvate + 2 H2O

2 Pyruvate + 2 H2OGlucoseNet

4 ATP formed – 2 ATP used 2 ATP

2 NAD+ + 4 e– + 4 H+ 2 NADH + 2 H+

The citric acid cycle (Kreb Cycle)

In the presence of O2, pyruvate enters the mitochondrion (matrix)

Pyruvate must be converted to acetyl CoA, which links the cycle to glycolysis

Generates 1 ATP, 3 NADH, and 1 FADH2 per turn

The NADH and FADH2 produced by the cycle relay electrons extracted from food to the electron transport chain


Animation: MitochondriaAnimation: Mitochondria

Fig. 9-10

CYTOSOL MITOCHONDRION

NAD+ NADH + H+

2

1 3

Pyruvate

Transport protein

CO2Coenzyme A

Acetyl CoA

Fig. 9-11

Pyruvate

NAD+

NADH

+ H+Acetyl CoA

CO2

CoA

CoA

CoA

Citricacidcycle

FADH2

FAD

CO22

3

3 NAD+

+ 3 H+

ADP + P i

ATP

NADH

The Pathway of Electron Transport

The electron transport chain is in the cristae of the mitochondrion

NADH and FADH2 donate electrons to the electron transport chain

Electrons drop in free energy as they go down the chain and are finally passed to O2, forming H2O


Electrons are passed through a number of proteins

The electron transport chain generates no ATP

The chain’s function is to break the large free-energy drop from food to O2 into smaller steps that release energy in manageable amounts


Electron transfer in the electron transport chain causes proteins to pump H+ from the mitochondrial matrix to the intermembrane space

H+ then moves back across the membrane, passing through channels in ATP synthase


VCAC: Cellular Processes: Electron Transport Chain: First LookVCAC: Cellular Processes: Electron Transport Chain: First Look

VCAC: Cellular Processes: ATP Synthase: The MovieTransport VCAC: Cellular Processes: ATP Synthase: The MovieTransport

Fig. 9-14INTERMEMBRANE SPACE

Rotor

H+

Stator

Internalrod

Cata-lyticknob

ADP+P ATP

i

MITOCHONDRIAL MATRIX

ATP Production by Cellular Respiration

Glycolysis- 2 ATP Citric Acid cycle- 2 ATP ATP Synthase- 32 or 34 Total- 38 ATP


Fermentation and anaerobic respiration

• Most cellular respiration requires O2 to produce ATP

• Glycolysis can produce ATP with or without O2 (in aerobic or anaerobic conditions)

In the absence of O2, glycolysis couples with fermentation or anaerobic respiration to produce ATP


Types of Fermentation

Two common types are alcohol fermentation and lactic acid fermentation

In alcohol fermentation pyruvate is converted to ethanol Yeast - in brewing, winemaking, and baking


In lactic acid fermentation, lactate is the end product

Fungi and bacteria - make cheese and yogurt Human muscle cells use lactic acid

fermentation to generate ATP when O2 is scarce


Fig. 9-19Glucose

Glycolysis

Pyruvate

CYTOSOL

No O2 present:Fermentation

O2 present:

Aerobic cellular respiration

MITOCHONDRION

Acetyl CoAEthanolor

lactateCitricacidcycle

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Chapter 9 Cellular Respiration: Harvesting Chemical Energy